Method for making diodes and products resulting therefrom



y 1961 J. M. N. HANLET 2,983,631

METHOD FOR MAKING DIODES AND PRODUCTS RESULTING THEREF'ROM Filed Jan. 30. 1959 2 Sheets-Sheet 1 INVENTOR JACQUES MARIE NOEL HANLET EW/M "M ATTORNEYS y 9, 1961 J. M- N. HANLET 2,983,631

METHOD FOR MAKING DIODES AND PRODUCTS RESULTING THEREFROM Filed Jan. 30. 1959 2 Sheets-Sheet 2 ESTABLIS H AND MAINTAIN ENCLOSE METAL BASE HIGH VACUUM IN VACUUM CHAMBER Sid HEAT SEMI-CONDUCTOR AND DEPOSIT ON METAL BASE AS A THIN LAYER APPLY POROU S CERAMIC EVAPORATE CONDUCTIVE LAYER OVER SEMI-CONDUCTOR LAYER METAL AND DEPOSIT OVER POROUS CERAMIC LAYER FILLING PORES WITH METAL REMOVE RESULTING MULTl-LAYER STRUCTURE AND USE AS DIODE PERFORATIONS IN LAYER (111) WITH METALHYIEXTENDING I- FILM AS THROUGH AND corrmcrmem) (ELECIRODE (w) DIELECTRIC FILM SEMI-CONDUCTOR 'f- R f .,,T (In) As "STRAINER" LAYER (11) CONDUCTIVE METAL BASE (1) INVENTOR JACQUES M. N. HANLET BY n @JM ATTORNEYS METHOD FOR MAKING DIODES AND PRODUCTS RESULTING 'II-IEREFROM lacqueseMariefNoel Hanlet, Santa Monica, Calif. as-

slgnor to, Societe dElectronique et dAutomatlsme, 'Courhevoie, Seine, France, a corporation of France Filed Jan. 30, 1959, Ser. No. 790,280 Claims priority, application France Feb. 10, 1958 13 Claims. (Cl. 117-200) The .presentinvention has for its object a process for making diodes and similar elements using the currentrectifying properties of semi-conductive crystals and par ticularly those of the semi-conductors of group IV of the classification ofjelements, such as germanium and silicon. .1- H a .Acfurther object. isj the production of such diodes which, though. made in a rapid and economical fashion, nevertheless offer intrinsically improved electrical performance when employed in circuits for currents of very highr-frequencies, such for example as commutation or switching circuits having great speed of operation.

-Still another object is the production of a diode structure comprising a semi-conductor obtained by the instant process, and. which includes a thin semi-conductive crystalline layer placed upon a polycrystalline conductive base, said'seini-conducting layer being covered with a dielectric. film forming a strainer or perforated layer, and a metallic film of counter-electrode applied over this dielectric layer and contacting the semi-conductive layerat a plurality of points of contact completed through the ope'nings in the strainer layer; a In such a structure,

- being a view in elevation *as"seen from Patented May 9,1961

rounds the end (if this shaft and tends normally to urge the shaft llatothe left, and it also acts upon shaft 11 through a jig or holder which is supported between the two shafts 11 and 11a. Thus, when magnet 13 is ener-' gized by alternating current, the two shafts and the jig connectingthem are subjected to vibratory movement asjsupports and eventually as bases for the diodes. Four crucibles 18 are mounted below this frame and mp it, while Fig, 2 is a view of the apparatus from above.

Theinventioln isfurtherj illustrated by Figs. 3 and 4. Fig. 3 is a' j-fl ow diagram which diagrammatically illustrates the order of steps involved in forming the, new

diode materials 'of the invention. Fig.1 4 is a diagram iiia'tic enlarged cross-sectional view of articles prepared in acepiaa'ace *With the invention, the plurality of layers involved 'Withtlie newarticles beingdesignatedby legends which indicate the materials involved. j

' A' vacuum 1,- havingconventional pumping equipnient notshowm-iseguipped at its upper part'with a receptacle,{containing enamel'granules 3 aridfcohnected hermeticallytq thejar by a coupling tube 5 ayalvejd beinginterpose'd inthe connection. Thejar l j is js eated upon and hermeticallysealed to the' base 6.

Mounted' upon the base Gwithin the jar lfis asu ga formed o f two vertical brackets 7 and 8 carrying aligned bearings and10 at their upperends. A shaft, 11 ex? t j j t hroughb earing 10 and "carries on its outer end a et' polepiece12'arranged.oppositean electroj hich is mounted outside'of the jar for turng th axis o f the bearings 9 and; 10; the ,pqlei 'withirithe field oft the: magnet 13 so he magnetahout its axis effects turning b'outfits-axi's Another "short shaft 11 hea-in est, and a return spring- 14 stir is set s "that atj the residual, gas pressure along the axis of the shafts.

This jig or holder is made up of a frame having two lateral uprights 15 and 16 between which are stretched metal conductor ribbons 17 which are 'to serve ported on base 6 at the four corners of the orthogonal projection of the frame on the plane of the crucibles. A second set of crucibles 20 is associated withthe set of; crucibles l8, for example off-set laterally from the set 18, as shown in Figure 2, where these sets are indicated in; dotted lines. Each set of crucibles can be heated by passage of an electric current supplied through conductor 19 for crucibles 18, and through conductor 21 forcrucibles 20. The upright bracket 8 is insulated from the base 6 at 22, and bracket 7 is grounded to the base. A current for heating the frame and the ribbons which it supports is supplied by connection 8a leading to the insulated upright 8.

The ribbous17 intended to form the base of the diodes are made of an alloy of iron and nickel, the coefiicient of expansion of which is strictly identical with that of germanium which will be used as the semi-conductor. Preferably, the surface of these ribbons has been preliminarily treated to cover it with a layer of alloy of gold and bismuth of several molecules in thickness, which alloy layer has been thermically treated on the ribbons. The system of crystallization of the nickel-iron alloy belongs to the same spatial group as that of germanium and, the ratio of meshes is a whole number. The gold-- bismuth alloy alsohas a crystal form comparable with that of the preceding but allows, further, at the time of the formation of the germanium crystalline layer, the attainment of an automatic alignment of the crystallographic axis 110 of the germanium with the crystallographic axis alignment of the alloy Au Bi, servingas an epitaxic reference which leads to a distribution of net like planes on the iron-nickel base which contains the axes100 and from whencea better orderedstat'e of the crystallography of the diodes is obtained. a

:The ribbons can have an individual width of 3 mm. and a length of lOtl minL, for example. A' grouping of 33 ribbons in the frame then forms a plane surface area of about 100 mm on the side. A mask M shown in Fig; 2, but omitted from Fig. 1 so as not to' obscure the drawing, -.can be placed over the ribbons and held by the frarneso as todeliniibor outlinetlie areas of the diodes; This :mask M may consist of"parallel"ribbons 23 stretchedtransversely to the'ribbons17 and theare'a of each diode can; for example, be reduced to'4. mm by having ribbons 23 of a width of about 11mm.\and" spaced apart aboutdl/s mm. With the above arrange: merit, oiiecam forexarnple,make simultaneouslll. 1309 to 1400 diodes, substantially iuniform dispersion characteristics, since they will be formed together by a common treatment, thus assuring them oftlie same characteristics of dimensions and crystallograp I As a specific example ofr theinstantproess, 300"m1l l-igrams ofdoped germanium is placed in eachofth'e four crucibles1 8." equal charge of analloy of'tin and' cadmium is-placedinfcruoibles{20. "Ajv clu u" A ot IO mm. of mercurv'is then'draWnbntheIjar i.

Thedi stance of the crucibles is rrbm was the "molecules. Theoccurrence of oxidation during the amount. The crucibles 18 are heated to 1400 C. until the germanium has substantially evaporated and deposited on the ribbons'17 which are maintained ata temperature close to theuteeue point, that is, about 325" C., by sup lying heating current to lead 8a. ;The alloys do not dilruse and their cr stalline structure is not modified; The germanium coating. is applied to a thickness of about microns, and the coating is quite uniform be cause of the uniform disposition of the crucibles with respect to theribbon assembly and the uniform temperature conditions. During the evaporation operation the electromagnet 13 is not energized; Without interrupting the vacc'um at this time and keeping the heating'reduced on the ribbons 17, the frame is turned through 180 so that the face covered with germanium may be turned up. This is done by turning the electro-mag'net 13' which is being fedby alter nating current to assure a lateral periodic vibration of' the frame carrying the ribbons 17. Then the valve 4 is opened to cause to fall upon the exposed area of rib; bons 17 a rain of granules of enamel 3. The receptacle 2 may contain an atmosphere of helium, for example. The granules of enamel have been screened'so as to present tor between the barrier and the resistance contact practically'r'nakes the storage capacity of the holesnegligibl'e. The thinner the layer of germanium the more the series resistance diminishes and it is entirely possible to make it of a value of some hundredths of an ohm. By reducing the diameter of the points of contact the capacity of the barrier is reduced and, consequently, the diodes obtained permit efficient rectification of very high rr equency currents. Further, the effect of temperature upon the inverse voltage is particularly reduced sinceiher'adiating surfaceof the counter-electrode is large as compared :with that of the points of contact. Finally, the fact that the operative process is carried on entirely in a controlled 1 vacuum assures the production of diodes with a surface grains of a diameter between 20 and 40 microns at most.

The material of the granules can be of the following composition (by way of illustration):

The granules, because of the vibration of the frame, are distributed over the ribbons in a layer which is very uniform. The enamel softens at the low temperature of strips 17 and is formed on the germanium as a coarse porous layer of a thickness of 10 to 25 microns.

The frame is then reversed to its first position, whereupon .the; excess granules fall, leaving the germaniumcovered surfaces of the ribbons covered with a veritable :strainer of enamel, the holes or pores of which, after heating, scarcely exceed 5 to 7 microns in diameter at the maximum; Further spreading of the granules and consequent reduction of the hole size can, if desired, be madeqbycontinued heating.

Q With the frame held stationary in its original position, the crucibles 2.0 are heated to. a temperature in the neighborhood of 850 C. toevaporate the alloy of tin and cadmium which deposits upon the strainer layer, andv this alloy deposit fills the holesof the porous layer and forms'wa counter-electrode layer. Each filled holeor pore in theporous layer leading to the germanium-covered portionsprovides a filamentary connection between the germanium-and the, counterrelectrode. The electro-rnagnet 13 is not energized during formation of the counter electrode. a a p {The ribbons 17, may now-be removed from the vacuum jar... If the'diode elements, are, tobe used separately, they are separatedfrom each other by severing the ribbons 17 along the, transverse areas which were shielded by the shielding strips 23z. 'Upon'providing the individual elements with conventional terminal connections, the diodes are'finished, I i H v The intrinsic characteristics of the diodes depend fundamentally on'the thickness of the layer of germanium and the'nuniber' of points of contactper unit areaof surface.

. It: is very evident that this thickness is adjusted by the 'is substan tially doubleithat o fthe resistance conba r entirely free of absorbed gas, thus increasing the quality of these products.

I claim:

1. A process for making multiple diodes on a common base, each diode comprising a metallic ba'se' having for'rned thereon a first layer of semi-conductorma terial selected from the group consisting of silicon and germanium, a second layer of porous ceramic'dielectric material, and a third layer of conductive metal, said process comprising enclosing a metallic ribbon in a vacuum chamber maintained at a pressure of theor'der of '10- of mercury, heating a semi-conductor ma terial within said chamber to produce thermal radiation of said material, subjecting said ribbon to said radiation through a shield to deposit a layer of said semi-conduc tor only upon spaced linear portions of said ribbon, heating said semi-conductor layer to effect crystallization thereof, applying a porous ceramic layer over said layer of semi-conductor material, and subjecting said ribbon to radiation froma source of vaporized metal transmitted through said shield to form separate conductive layers over the linear sections of said ribbons which arecovere'd by said semi-conductor layer.

2. A-process according to claim 1 wherein the porous dielectric layer is formed by flowing granulesof enamel over the surfaceof said ribbon, then heating thBH'ibbOIlxtO melt the granules. I 3. A process according to claim 2, in whichthe-dielectric granules have a: grain size between 20 and- 40 microns, the porous ceramic layer finally obtained; having athickness'of the order of 25 microns. 1 4 A process according. to claim 1, in, which the said ribbonis initially coated with. an alloy:v of gold-bismuth. 5. A processaccording-toclaim,4, in-which theribbon I is of metal selected from theugroup consisting OfIiIOIl and nickel. I r

6. A process according to claim 1, inwhich the com ductive layer is made of an alloy of cadmium-ting 1 l 7. A process according to claim 1, in which alplurality of metallic ribbons are enclosed within said vacuum chamher and supported in a common plane upon a frame'which can-be inverted,.yand-said shield comprisesa plurality of spaced parallel -ribbons arranged'transversely of, said metallic ribbons. s l

M 8. Azpr'ocess according to claim 7, wherein said dielectric layer is formed by flowing granules of enamel over the surface, of said metallic ribbons supported uponsaid a aem a including the step of vibratingfsaid frame to effect ,unifor'rnldistributionfof the ,granules over-lithe p faces of'said ribbons.

. s 9. A prOcess according to claim wherein saidv of enamel are heated by passingjelectric current'through said ribbon. v r

lOIA process asclaimedin claim 1 whereinthe porous dielectric 'layerfis formed by flowing granules of enamel 0 overthe surface, of sai'd ribbon, and the enamel is heated a point or contact, and the approximate diameter of this tact oiiit; The of the barrier isabout 300 to melt the granules, said heating being continuedlto spread the: granules "and reduce the hole size of'the result! ing porous layer to less than about 7 microns in diameter. I ll.-

process asclaimed in claim 1 wherein the porous dielectric layer is formed by, flowing granules; of enamel over the surface of said metallic ribbon, said ribbon is vibrated to obtain uniform distribution of the granules over the ribbon and the distributed granules are heated to melt them and form a porous dielectric layer.

12. A diode comprising a metallic base of conductive metal having formed thereona plurality of separate thin layers, the first layer being substantially continuous and formed of semi-conductor material selected from the group consisting of silicon and germanium, the second layer being porous and formed of ceramic dielectric material and the third layer being substantially continuous and formed of conductive metal, the pores of said second layer being filled with the metal of said third layer, the metal filling said pores being in electrical contact with the top surface of said first layer, said metal filling said pores further being integral with the metal of said third layer.

13. A diode comprising a metallic base of conductive metal, a layer of gold-bismuth alloy several molecules in thickness formed upon said base, a layer of semi-conductive material selected from the group consisting of silicon and germanium formed upon the gold-bismuth alloy coated base surface, said semi-conductive layer being substantially continuous and of a thickness of about 5 microns, said conductive metal of said base being an iron-nickel alloy having a coefficient of expansion identical to the coefficient of expansion of said semi-conductive material, a porous layer of ceramic dielectric material formed upon said semi-conductive material layer, said porous layer having a thickness of about 10 to 25 microns With the pores thereof being less than about 7 microns in diameter, and a substantially continuous top layer formed upon said porous layer of cadmium-tin alloy, the pores of the porous layer being filled With the alloy of said top layer, the alloy filling said pores being in electrical contact with the top surface of said semi-conductive material layer, said alloy filling said pores further being integral with the alloy of said top layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,702,259 Sommer Feb. 15, 1955 2,766,144 Lidow Oct. 9, 1956 2,768,098 Hoppe Oct. 23, 1956 2,789,062 Cusano et al Apr. 16, 1957 2,818,831 Vine Jan. 7, 195 8 

1. A PROCESS FOR MAKING MULTIPLE DIODES ON A COMMON BASE, EACH DIODE COMPRISING A METALLIC BASE HAVING FORMED THEREON A FIRST LAYER OF SEMI-CONDUCTOR MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILICON AND GERMANIUM, A SECOND LAYER OF POROUS CERAMIC DIELECTRIC MATERIAL, AND A THIRD LAYER OF CONDUCTIVE METAL, SAID PROCESS COMPRISING ENCLOSING A METALLIC RIBBON IN A VACUUM CHAMBER MAINTAINED AT A PRESSURE OF THE ORDER OF 10-6MM. OF MERCURY, HEATING A SEMI-CONDUCTOR MATERIAL WITHIN SAID CHAMBER TO PRODUCE THERMAL RADIATION OF SAID MATERIAL, SUBJECTING SAID RIBBON TO SAID RADIATION THROUGH A SHIELD TO DEPOSIT A LAYER OF SAID SEMI-CONDUCTOR ONLY UPON SPACED LINER PORTIONS OF SAID RIBBON, HEATING SAID SEMI-CONDUCTOR LAYER TO EFFECT CRYSTALLIZATION THEREOF, APPLYING A POROUS CERAMIC LAYER OVER SAID LAYER OF SEMI-CONDUCTOR MATERIAL, AND SUBJECTING SAID RIBBON TO RADIATION FROM A SOURCE OF VAPORIZED METAL TRANSMITTED THROUGH SAID SHIELD TO FORM SEPARATE CONDUCTIVE LAYERS OVER THE LINEAR SECTIONS OF SAID RIBBONS WHICH ARE COVERED BY SAID SEMI-CONDUCTOR LAYER. 